Improve poor security recommendation in docs

As reported in #9960, the current documentation recommends an insecure practice for
key generation from a password (a single round of SHA-256). The modified documentation
uses ActiveSupport::KeyGenerator to perform proper key stretching.
Fixes skipping object callback filters

This allows you to skip callbacks that are defined by objects, e.g. for
`ActionController`:

    skip_after_filter MySpecialFilter

Previously this didn't work due to a bug in how Rails compared callbacks
in `Callback#matches?`. When a callback is compiled, if it's an object
filter (i.e. not a method, proc, etc.), `Callback` now defines a method on
`@klass` that is derived from the class name rather than `@callback_id`.
So, when `skip_callback` tries to find the appropriate callback to
remove, `Callback` can regenerate the method name for the filter
object and return the correct value for `Callback#matches?`.
Alignment
Adding documentation to actionview so that the big picture of the
renderer is clearer.
symbolize_keys => symbolize_keys! on new hash;

"There're" => There are for better readability
Revert "Merge pull request #10183 from jholton/fix_association_auto_save"

This reverts commit e8727d37fc49d5bf9976c3cb5c46badb92cf4ced, reversing
changes made to d098e1c24bc145e0cc14532348436e14dc46d375.

Reason: it broke the mysql build
Merge branch 'master' of github.com:rails/rails
Merge pull request #10265 from wangjohn/documenting_actionview

Adding documentation to Renderer
Merge pull request #10267 from vipulnsward/use_destructive_method

symbolize_keys => symbolize_keys! on new hash; change sentence
fix respond_to? for non selected column

fixes #4208

If a query selects only a few columns and gives custom names to
those columns then respond_to? was returning true for the non
selected columns. However calling those non selected columns
raises exception.

    post = Post.select("'title' as post_title").first

In the above case when `post.body` is invoked then an exception is
raised since `body` attribute is not selected. Howevere `respond_to?`
did not behave correctly.

    pos.respond_to?(:body) #=> true

Reason was that Active Record calls `super` to pass the call to
Active Model and all the columns are defined on Active Model.

Fix is to actually check if the data returned from the db contains
the data for column in question.
Merge pull request #10211 from neerajdotname/4208

fix respond_to? for non selected column
Typo Fix in AR CHANGELOG [ci skip]
Merge pull request #10273 from prathamesh-sonpatki/AR-typos

Typo Fix in AR CHANGELOG [ci skip]
Rewrites a CHANGELOG entry.

The entry is basically copy & paste of the commit message, but the CHANGELOG
has a different purpose than Git history, it just communicates what is new:

* No need to explain why did the bug happen (unless it is truly relevant).

* No need to explain how was the bug fixed.

* Whether the user gives new names to columns does not really matter, use of
  select to cherry-pick a column for example also presented that behaviour.
  Non-selected attributes are the key, either because they were not included
  in the selected list, or because they were but with a different alias.

* In the case of an attribute alias, what you really want to depict is that
  respond_to? returns false for the original attribute name.
if singletons belong to the contract, test them

Object#respond_to? returns singletons and thus we inherit that contract.
The implementation of the predicate is good, but the test is only
checking boolean semantics, which in this case is not enough.
Increase readability of ternary statement in build method
Merge pull request #10275 from buddhamagnet/master

Increase readability of ternary statement in build method
fix typos
Merge pull request #10280 from vipulnsward/fix_typos_temp

fix typos [ci skip]
Removing tests for deprecated options in active support. The
+use_full_path+ option was removed in 3b3790a4 and passing the template
handler to render was deprecated in 43d27e91.